Description of Related Art
The current process for chip making is called deep-ultraviolet lithography (DUV), which is a photography-like technique that focuses light through lenses to expose the raw circuit material and the accompanying photomask. Subsequent etching and chemical processing carves circuit patterns on the circuit material, such as a silicon wafer. The key to creating more compact and powerful microprocessors is the size of the light's wavelength. The shorter the wavelength of light that is used, the more transistors that can be etched onto a given area of a silicon wafer's surface. As of 2001, deep-ultraviolet lithography used a wavelength of 230 nanometers (nm) and it is anticipated that that DUV technology will permit features as small at about 100 nm. The next generation of lithography under development is known as Extreme Ultraviolet Lithography (EUVL).
EUVL uses a light source with a wavelength of 13.5 nanometers (nm). This wavelength may be obtained from plasma-based systems using a variety of technological approaches. In U.S. Pat. No. 6,493,423, a plasma generating gas is exposed to a high energy pulsed laser producing EULV in the desired range. The plasma-generating gas may be a gas such as xenon. When the laser hits the xenon gas, it heats the gas up and creates plasma. Once the gas is plasmatized, electrons are emitted from the plasma and the plasma radiates light at 13.5 nm. The problem with creating the plasma with a laser is that lasers of sufficient power are expensive, both to purchase and to operate. It order to develop EUVL commercially, is will be necessary to provide an inexpensive source of plasma.
For many years, it has been known that x-rays and high energy ultraviolet radiation could be generated by a plasma source referred to as z-pinch. In a z-pinch plasma source an electric current passes between two electrodes, through a plasma generating gas, in one of several possible configuration. The magnetic field created by the flowing electric current accelerates the electrons and ions in the plasma into a tiny volume with sufficient energy to cause substantial stripping of outer electrons from the ions and a consequent production of x-rays and high energy ultraviolet radiation. Typical prior art plasma z-pinch devices, such as presented in Asmus et al., U.S. Pat. No. 4,889,605 and Stromberg et al., U.S. Pat. No. 4,899,355, can generate large amounts of radiation suitable for proximity x-ray lithography. However, these devices are limited in repetition rate due to large per pulse electrical energy requirements, and short lived internal components. The stored electrical energy requirements for these systems range from 1 kJ to 100 kJ. The repetition rates typically did not exceed a few pulses per second. Further, the problem with electrodes, in the plasma environment, is that electrodes, particularly the anode, suffer from a high erosion rate due to particle and heat fluxes resulting in low efficiency and short lifetimes.
One of the main obstacles now in achieving EUVL commercial goals in discharge produced plasma (Hereinafter referred to as “DPP”) devices is electrode erosion at the required high power necessary for high volume manufacturing (Hereinafter referred to as “HVM”). Existing facilities are based on 50 years old traditional ideas when first devices for production of 14 MeV neutrons for thermonuclear fusion research were studied. However, these facilities were never intended for use as powerful machines operating at high frequency. Only in recent years has there been research from various groups to develop devices to obtain 100–200 W radiation sources and now meet serious problem with material erosion. This is due to the very small efficiency, ζ to transfer stored energy in 13.5 nm radiation: as ζ≈0.1% the required electric power should be about 100 kW. If the plasma-facing component (PFC) surface has an area less 100 cm2 the heat load onto surface exceeds 1 kW/cm2 which is difficult to remove by conventional methods as it is well studied in fusion reactor and space research investigations.